1. Field of the Invention
The present invention relates to a paper magazine for a recording paper roll such as a roll of a film-like thermal recording paper, and to a recording paper roll for keeping humidity of the paper magazine at a constant level.
2. Description of the Related Art
For example, in a color thermal printer, a color thermal recording paper is used and three colors are recorded in order to record a full color image. As shown in FIG. 15, the color thermal recording paper 110 is provided with a cyan heat sensitive color layer 102, a magenta heat sensitive color layer 103, an yellow heat sensitive color layer 104, and a protect layer 105 which are stacked in order on a support member 101 utilizing a resin-coated paper. The yellow heat sensitive color layer 104, which is a the uppermost layer among the color layers, has the highest heat sensitivity. The cyan heat sensitive color layer 102, which is a the lowermost layer, has the lowest heat sensitivity. Each of the color layers is recorded in order from the uppermost layer. After a yellow image is recorded, near ultraviolet radiation of 420 nm is applied to fix the yellow image optically. Accordingly, non-colored ingredient of the yellow heat sensitive color layer 104 is not colored when thermal recording for the magenta heat sensitive color layer 103 is carried out. Similarly, after the recording for the magenta hest sensitive color layer 103 was carried out, ultraviolet radiation of 365 nm is applied to fix a magenta image optically.
For a personal-use thermal printer in which the amount of prints is small, cut papers are used. The paper is cut in a predetermined size beforehand. However, for a business-use thermal printer in which the amount of prints is large, it is suggested that a roll-like color thermal recording paper is used and cut as a sheet after recording. For example, Japanese Patent Laid-Open Publication No. 6-79893 discloses a color thermal printer in which a pinch roller and a thermal head are disposed at an outer periphery of a platen roller. The color thermal recording paper is moved half round the platen roller so as to be folded back in a U-like shape. Successively, the color thermal recording paper is sent to an optical fixing unit. The fixing unit is constituted of two ultraviolet lamps and arranged such that the ultraviolet radiation from the lamp crosses the recording paper. One of the ultraviolet lamps is for fixing the yellow image and applies the near ultraviolet radiation of 420 nm to the recording paper. The other of the ultraviolet lamps is for fixing magenta and applies the ultraviolet radiation of 365 nm to the recording paper. At the downstream side, a cutter is disposed in front of a paper discharge port.
In this color thermal printer, the color thermal recording paper drawn out from the thermal recording paper roll is advanced and pulled back at a printing section. The advancement and the pulling back are performed one after the other in order to record a full color image in three-color frame sequential process. At the outset, the recording paper is advanced from the paper roll by a predetermined amount. After that, the platen roller and the paper roll are rotated in the reverse direction to pull back the recording paper. During the first pulling back, the recording paper is pressed and heated with the thermal head to record a yellow image in a record area line by line.
The recording paper is advanced from the paper roll again. At this time, the ultraviolet lamp for yellow image is turned on to fix the yellow heat sensitive color layer. During the second pulling back of the recording paper, the magenta image is recorded with the thermal head. After that, the recording paper is advanced again. At this time, the ultraviolet lamp for the magenta image is turned on to fix the magenta heat sensitive color layer. During the third pulling back, the cyan image is recorded in the cyan heat sensitive color layer one line by one line. After recording the cyan image, the recording paper is advanced from the paper roll and cut with the cutter as a sheet. The sheet is discharged and the thermal recording of one sheet is completed.
In case of the color thermal printer using the roll-like color thermal recording paper as described above, an amount of recording sheets cut from a thermal recording paper roll is very large so that it is possible to carry out a great number of prints without exchange of the thermal recording paper roll is. However, if the thermal recording paper roll taken out from a light shielding sack, and a dampproofing sack and so forth is set in the color thermal printer for a long time, the paper roll is exposed to the light entering the thermal printer so that the color ability thereof is reduced. Moreover, the color property of the recording paper is changed by the influence of humidity in the color thermal printer. Thus, it becomes impossible to color in a desired density. Further, if the ultraviolet ray from a fluorescent lamp and so on enters the color thermal printer, the color property is changed also at this time.
In order to prevent the color property of the recording paper from changing, it is considered, for example, that the remainder of the paper roll is taken out from the color thermal printer and contained in a dampproofing sack, a dampproofing box and so forth whenever the printing is over. However, it takes a lot of time and labor to do that. Further, the photosensitive thermal recording paper is exposed to the outside light in the course of containing it.
Thus, it is desirable to protect the thermal recording paper roll against the humidity and ultraviolet rays by containing it in a paper magazine. In this case, it is desired that after the printing was over, the recording paper sent in the color thermal printer is drawn back in the paper magazine and a draw-out mouth of the paper magazine is closed.
By using such a paper magazine, the influence of ultraviolet rays may be prevented. However, it is difficult to shut the paper magazine tightly and perfectly so that little air enters the paper magazine. Of course, the draw-out mouth is opened during the printing so that the air enters the paper magazine during that operation. If the recording paper is contained in the paper magazine for long time, humidity for the recording paper changes gradually due to the air entering the paper magazine. At this time, the influence of humidity on the recording paper is different in accordance with each portion thereof. In other words, the influences of humidity for a roll portion and a leading edge portion apart from the roll portion are different.
At the roll portion, a color face of the color thermal recording paper contacts a rear face of one-round inner color thermal recording paper so that the color face is hardly affected by damp by the air entering the paper magazine. However, at the leading edge portion apart from the roll portion, the color face is exposed in the paper magazine so that the color face is affected by the damp in the paper magazine. When the printing is carried out for such a color thermal recording paper, color densities are different relative to the leading edge portion affected by the damp and the roll portion hardly affected by the damp.
In the case of using the paper magazine, it is desirable that a main body of the paper magazine is made of light shielding material so as not to expose the thermal recording paper roll to the natural light and the light from a fluorescent lamp. However, if the paper magazine is made of the light shielding material, there arises a problem in that the remainder of the paper roll contained in the magazine can not be observed from the outside. If the remainder of the paper roll is not known, it is impossible to foresee the exchange timing thereof. Thus, there arise problems in that the recording paper runs out during the printing, and that preparation of the paper roll is behind.
By the way, FIG. 16 is a graph showing a color property of the color thermal recording paper. Full lines show the color properties at 60% RH which is normal humidity at 25.degree.C. Under an environment that the humidity is higher than that, the amount of moisture contained in the recording paper increases. As shown by dashed lines in FIG. 16, if a prescribed thermal energy is applied to the recording paper, each color of yellow(Y), magenta(M) and cyan(C) colors in paler density than an original color density. Under an environment that the humidity is lower than the normal humidity, the amount of moisture contained in the recording paper decreases rather than an amount relative to the normal humidity. In this case, as shown by broken lines in FIG. 16, if a prescribed thermal energy is applied to the recording paper, each color of Y, M and C colors in darker density than the original color density.
When the thermal recording paper roll is contained in the paper magazine, as the paper magazine does not have humidity adjusting ability, the paper roll is not kept at the normal humidity. For example, if an outer environment of the paper magazine is in a high humidity state or a low humidity state when the paper roll is set in the paper magazine, the inside of the paper magazine is adapted to be kept in a state of high humidity or low humidity. Further, of course, the draw-out mouth for the recording paper is opened during the printing. Thus, the damp or the dry air enters the paper magazine through the draw-out mouth when the printing is carried out for a long time. By the outside air entering the magazine, the recording paper comes into a state of high humidity or low humidity gradually while it is contained in the paper magazine.
A conventional paper magazine is constituted of a magazine main body formed with an elongated paper feed mouth and a lid rotatably attached to the magazine main body via a hinge. A recording paper roll is wound around a cylindrical core made of paper or plastic. When the paper roll is loaded in the paper magazine, a pair of flanges are attached to the core. Each of the flanges is provided with a shaft portion passing through a flange portion. A support portion is provided on an inside of the flange portion and fitted into the core. The shaft portion is put in a bearing of the magazine main body. The lid is closed after loading the paper roll.
However, in the conventional paper magazine, if there is looseness between the bearing of the magazine main body and the flange, the recording paper drawn out from the paper magazine is shifted from the regular position in width direction. Due to a gap of position, an image is not correctly printed at a predetermined position of the recording paper.
Moreover, the paper roll is superfluously rotated by inertia after the drawing operation of the recording paper was stopped. And the paper roll is sometimes rotated by vibration and so forth during the printing. Thus, conventionally, a clutch device such as a friction clutch and so on is attached to recording paper roll to give a back tension so that the paper roll is prevented from rotating inadvertently. However, upon using the clutch device, the structure of the paper magazine becomes complicated and the cost of it increases.